Facebook owns all your pictures. If you agree to their terms of service they can use and sell your pictures however they want. Plus they are allowed to keep a copy of all your removed pictures. So if one day your face is on a billboard in an add you didn´t agree to. Facebook had the right to do that. And their stalking is even creepier.
They map your face for facial recognition/ tagging. And they map all your use of GPS, WIFI and Bluetooth to track your phyiscal movements. And much much more.